The present invention relates to a forming die apparatus that presses a workpiece using two dies that are brought toward and away from each other and to a die member of the forming die apparatus.
Typically, separators used in fuel cells are formed by, as shown in FIG. 6, providing a plate 31 made of a corrosion-resistance metal, such as titanium, with contiguous grooves and protrusions 32. The grooves and protrusions 32 define passages thorough which coolant or gas of hydrogen or oxygen flows.
When forming such a separator for a fuel cell, a forming die apparatus as shown in FIG. 7 is conventionally used, for example. The forming die apparatus includes a lower die 33 and an upper die 34. The lower die 33 has on the upper surface a die surface 331 with grooves and protrusions, and the upper die 34 has on the lower surface a die surface 341 on which grooves and protrusions are formed to correspond to the die surface 331 of the lower die 33. The upper die 34 is arranged above the lower die 33 to be brought toward and away from the lower die 33. With a plate 31, which is a workpiece, placed on the die surface 331 of the lower die 33, the upper die 34 is brought toward the lower die 33 to press the plate 31 between the die surfaces 331, 341 of the dies 33, 34, so that the grooves and protrusions 32 are formed on the plate 31.
When producing the lower die 33 and the upper die 34 of the forming die apparatus, the surface of a die material made of super hard metal, such as high-speed steel, is cut to form the die surfaces 331, 341 having grooves and protrusions. When forming the die surfaces 331, 341, a cutting tool is used to cut the die material along a direction in which the grooves and protrusions on the die surfaces 331, 341 extend. Since the die material is made of super hard metal, the cutting tool becomes dull at an early point due to wear. Thus, it is difficult to continuously cut a long distance in the extending direction of the grooves and protrusions on the die surfaces 331, 341. If a worn cutting tool is replaced by a new cutting tool in the middle of cutting operation, the shape of a surface being cut significantly changes between before and after the replacement. This is highly likely to degrade the accuracy of the die surfaces 331, 341.
To deal with such a problem, a forming die apparatus as illustrated in FIG. 8 has conventionally been proposed. The forming die apparatus has a lower die 33 formed by die members 35, which are separate rectangular columns. The die members 35 are assembled on a base 36 and fitted in a frame 37. According to this configuration, limited parts of the end faces of the die members 35 are cut individually. Thus, problems due to wear of the cutting tool are less likely to occur. In addition, the die surface 331 with grooves and protrusions can be easily formed by joining the cut surfaces. Although not illustrated, the upper die of the forming die apparatus is configured by assembling die members as in the case of the lower die 33.
On the other hand, Japanese Laid-Open Patent Publication No. 2008-296262 discloses a press machine of die-quench method, in which heated steel material is pressed by upper and lower dies. The lower die of the press machine is formed by separate die blocks, so that expansion and contraction of the lower die as a whole due to temperature changes are suppressed. The die blocks are arranged side by side on a base with a clearance between the die blocks. In press operation, thermal expansion of the die blocks is absorbed by the clearances between the die blocks.